Droplet solidification modes

Figure 3.23. Schematic and micrograph of spreading, breakup and solidification modes of liquid metal droplets impinging on a cold surface. (a)-(d) Pancake pattern regularly shaped disks with or without corona, (e)-(h) Flower pattern irregularly shaped platelets with or without corona. (Micrograph reprinted with permission from Ref. 403 and 407. Courtesy of Dr. J. M. Houben, Eindhoven University of Technology, Netherlands and courtesy of Dr. Seiji Kuroda, National Research Institute for Metals, Japan.)...

In both atomization modes, as thin unstable ligaments, and/ or sheets disintegrate into round droplets, atomization gas may plausibly be trapped into the droplets under certain conditions. For alloys with alloying elements which readily react with atomization gas, for example, oxidize to form refractory oxides, solidification may be delayed and spheroidization is prevented so that rough flakes may form. For such alloys, the atmosphere in the spray chamber must be inert and protective to avoid the formation of any refractory and to foster spheroidal shape of droplets. 

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